Sir Richard Branson reportedly faces relinquishing control of airline Virgin Atlantic for the first time as America's largest airline made a secret takeover approach.

Delta Air Lines is understood to have offered to buy Singapore Airlines' 49% holding in Virgin, The Sunday Times said.

If it succeeds, Delta's European partner Air France-KLM may then buy part of Sir Richard's 51% stake, leaving the entrepreneur without majority control of the airline.

Sir Richard, who set up the airline in 1984, is said to have been weighing its future for several years, appointing Deutsche Bank two years ago to examine offers.

Delta and Air France-KLM came close to a deal in February 2011 but discussions broke down over price and Sir Richard's rights over the Virgin brand.

Virgin, which has its headquarters at Gatwick, has a fleet of 40 aircraft and flies around six million passengers a year to long-haul destinations. It posted a pre-tax loss of £80 million in the 12 months to the end of February.

Singapore paid £600 million for its stake in 1999 and there is no certainty a deal would be reached.

Earlier this year, British Airways expanded as it bought BMI British Midland, the second-largest Heathrow operator, giving it more than 50% of the crowded airport's take-off and landing slots.

Delta is America's biggest carrier by the number of passengers, carrying about 160 million a year compared with United Airlines' 140 million.